2.1: Models of bonding and structure

Ionic compounds

a chemical compound consisting of positively charged ions (cations) and negatively charged ions (anions) held together by strong electrostatic forces

why high melting point

build up into a strong lattice. Ionic compounds have high melting points as considerable energy is required to overcome these forces of attraction.

polyatomic ions

ions composed of two or more atoms that are covalently bonded together and carry an overall electrical charge, where the charge is often spread (delocalized) over the whole ion

Lattice

A three-dimensional regular repeating arrangement of ions, atoms or molecules in a crystalline solid.

lattice enthalpy

enthalpy change that occurs when one mole of an ionic compound is broken apart into its constituent gaseous ions under standard conditions.

hydration enthalpy

enthalpy change that occurs when one mole of gaseous ions dissolves in sufficient water to form an infinitely dilute aqueous solution under standard conditions.

are ionic compounds conductive

when solid no. when molten yes (ions free to move) where they are chemically

decomposed at the respective electrodes.

Covalent bonding

Covalent bonding involves the sharing of one or more pairs of electrons so that each atom in the molecule achieves a noble gas configuration. electrons are shared and attracted electrostatically by positive nuclei, resulting in a directional bond between the atoms to form a molecule.

octet rule

atoms tend to form chemical bonds in such a way that each atom has eight electrons in its outermost electron shell, giving it the same electron configuration as a noble gas

coordination bond

When both the electrons in the shared pair can originate from the same atom